The present invention generally pertains to the delivery of ophthalmically acceptable pharmaceutically active agents to the back of the eye. More particularly, but not by way of limitation, the present invention pertains to apparatus and methods for sub-Tenon delivery of a drug depot to the posterior segment of a human eye proximate the macula.
Several diseases and conditions of the posterior segment of the eye threaten vision. Age related macular degeneration (ARMD), choroidal neovascularization (CNV), retinopathies (e.g., diabetic retinopathy, vitreoretinopathy), retinitis (e.g., cytomegalovirus (CMV) retinitis), uveitis, macular edema, and glaucoma are several examples.
Age related macular degeneration (ARMD) is the leading cause of blindness in the elderly. ARMD attacks the center of vision and blurs it, making reading, driving, and other detailed tasks difficult or impossible. About 200,000 new cases of ARMD occur each year in the United States alone. Current estimates reveal that approximately forty percent of the population over age 75, and approximately twenty percent of the population over age 60, suffer from some degree of macular degeneration. xe2x80x9cWetxe2x80x9d ARMD is the type of ARMD that most often causes blindness. In wet ARMD, newly formed choroidal blood vessels (choroidal neovascularization (CNV)) leak fluid and cause progressive damage to the retina.
In the particular case of CNV in ARMD, two main methods of treatment are currently being developed, (a) photocoagulation and (b) the use of angiogenesis inhibitors. However, photocoagulation can be harmful to the retina and is impractical when the CNV is in proximity of the fovea. Furthermore, photocoagulation often results in recurrent CNV over time. Oral administration of anti-angiogenic compounds is also being tested as a systemic treatment for ARMD. However, due to drug-specific metabolic restrictions, systemic administration usually provides sub-therapeutic drug levels to the eye. Therefore, to achieve effective intraocular drug concentrations, either an unacceptably high dose or repetitive conventional doses are required. Various implants have also been developed for delivery of anti-angiogenic compounds locally to the eye. Examples of such implants are disclosed in U.S. Pat. Nos. 5,824,072 to Wong, U.S. Pat. No. 5,476,511 to Gwon et al., and U.S. Pat. No. 5,773,019 to Ashton et al.
In addition, it is known to use a straight, ⅝ inch long, 25 gauge needle to perform sub-Tenon injection of corticosteroids for the treatment of posterior uveitis or macular edema associated with uveitis or anterior segment surgery. See Uveitis: A Clinical Approach to Diagnosis and Management (Second Edition), Ronald E. Smith and Robert A. Nozik, 1989, pp. 63-68; xe2x80x9cEchographic Localization of Corticosteroids After Periocular Injectionxe2x80x9d, William R. Freeman, Ronald L. Green, and Ronald E. Smith, American Journal of Ophthalmology 103:281-288, March 1987. In such methods, a physician attempts to dispose the tip of the needle near the macula but without penetrating the posterior ciliary arteries or the optic nerve. However, because the physician cannot see the tip, as well as movement of the eyeball within the orbit due to contact with the straight needle, it is very difficult to precisely place the tip at the desired location near the macula. For the same reasons, it is also very difficult to determine whether the tip is correctly positioned below the Tenon""s capsule. Such methods do not insure a consistent delivery of a specific quantity of drug to a region over the macula. In fact, the literature reports that only about 57 percent of injections using this method result in drug being placed in the sub-Tenon space overlying the macular area. xe2x80x9cEchographic Localization of Corticosteroids After Periocular Injectionxe2x80x9d, pp. 283-285. In addition, moving a straight needle along the curved surface of the sclera causes xe2x80x9ctentingxe2x80x9d or stretching of the overlying Tenon""s capsule. Such movement may cause penetration of the Tenon""s capsule, allowing drug to be injected into surrounding tissues. Furthermore, such movement may also cause inadvertent penetration of the sclera, resulting in injection of drug into the vitreous cavity. More importantly, penetration of the sclera may result in significant damage to the eye or even a loss of sight. Documented complications of such penetrations include orbital hemorrhage, central retinal vein occlusion, and central retinal artery occlusion.
Referring to FIG. 6, it is also known to use a blunt 19 gage cannula 200 having a hub 201, a straight proximal portion 202, and an angled distal portion 204 to perform sub-Tenon injection of anesthesia for cataract and vitreoretinal surgery. See xe2x80x9cLocal Anesthesia for Vitreoretinal Surgeryxe2x80x9d, Calvin E. Mein and Michael G. Woodcock, Retina 10: 47-49, 1990; xe2x80x9cOcular Anesthesia for Cataract Surgery: A Direct Sub-Tenon""s Approachxe2x80x9d, Ophthalmic Surgery 21:696-699, 1990; xe2x80x9cSingle Quadrant Sub-Tenon""s Bock: Evaluation of a New Local Anaesthetic Technique for Eye Surgeryxe2x80x9d, Anaesthesia and Intensive Care 24: 241-244, April 1996. However, such cannulae also suffer from the above-described xe2x80x9ctentingxe2x80x9d and penetration problems if used to deliver drugs into the sub-Tenon""s space above the macula.
It is also known to use a gently curved cannula 210 as shown in FIG. 7 to perform sub-Tenon injection of anesthesia for cataract surgery. See xe2x80x9cCurved, SubTenon Cannula for Local Anesthesiaxe2x80x9d, Julian D. Stevens, Ophthalmic Surgery, 24:121-122, February 1993. However, this cannula also suffers from the above-described xe2x80x9ctentingxe2x80x9d and penetration problems if used to deliver drugs into the subTenon""s space above the macula.
It is also known to use a 24 gauge cannula that has a straight proximal portion and a curved distal portion that is disposed at a 90 degree angle to the straight portion to inject a local anesthetic solution below the Tenon""s capsule. The straight portion has a length of 5 mm. The curved portion has a radius of curvature of 14 mm and an arc length of 27 mm. See xe2x80x9cA Modified Sub-Tenon""s Cannula for Local Anesthesiaxe2x80x9d, P. Muthusamy and Richard F. Hommersom, Asia-Pacific Journal of Ophthalmology, Volume 8, No. 3 (July 1996). However, because of its geometry, this cannula is not suitable for the delivery of drugs in the form of suspensions, emulsions, ointments, or gels, or drugs in such forms including bioerodable polymers or non-bioerodable polymers.
Therefore, a need exists in the field of ophthalmology for improved apparatus and methods for sub-Tenon delivery of a drug depot to the posterior segment of a human eye proximate the macula that do not suffer from the above-described limitations. The improved apparatus and methods should be safe for the patient, easy for the physician to use, capable of delivering a wide spectrum of formulations, and capable of being performed in an outpatient setting.
One aspect of the present invention comprises a cannula including a distal portion having a radius of curvature substantially equal to a radius of curvature of a globe of the human eye, a proximal portion, and a bend separating the distal portion and the proximal portion. A tangent of the distal portion at the bend is disposed at an angle of no more than about 56 degrees with respect to the proximal portion.
In another aspect, the present invention comprises a method of delivering a drug to the human eye. A cannula is inserted below the Tenon""s capsule and above the sclera of the human eye at a point posterior to a limbus of the eye. The cannula includes a distal portion having a radius of curvature substantially equal to a radius of curvature of the globe of the human eye. A drug is injected through the cannula to form a drug depot on an outer surface of the sclera. The drug comprises a pharmaceutically active agent selected from the group consisting of 4,9(11)Pregnadien-17xcex1,21-diol-3,20-dione and 4,9(11)-Pregnadien-17xcex1, 21-diol-3,20-dione-21-acetate.
In another aspect, the present invention comprises a cannula including a hub for removably coupling to a syringe, a proximal portion, and a distal portion. The distal portion has a tip, an orifice proximate the tip, and a radius of curvature substantially equal to a radius of curvature of the globe of the human eye. The part of the distal portion proximate the tip comprises a plastic.